Process of producing beryllium metal powders



United States Patent Int. Cl. (:23!) 35/00,- B22f 9/00 US. Cl. 148-63 9 Claims ABSTRACT OF THE DISCLOSURE A method of producing beryllium metal powders substantially devoid of beryllium oxide wherein the beryllium metal powders are milled in a non-halogenated hydrocarbon vehicle and subsequently the powders are separated from the vehicle. The powders can then be exposed to air under controlled conditions to produce non-pyrophoric beryllium metal powders which will not combust at normal atmospheric conditions.

This application is a continuation-iu-part of copending applications Ser. No. 302,828, filed Aug. 19, 1963, and now abandoned, and Ser. No. 418,578, filed Nov. 20, 1964, and now abandoned.

This invention relates to a novel method of producing beryllium metal powders and, in particular, sub-sieve powders having a minimum of deleterious contaminants and wherein the beryllium metal powders produced are substantially devoid of beryllium oxide and have a protective surface resistant to catastrophic oxidation when exposed to the air and are capable of being handled in ambient conditions without the necessity of an inert atmosphere.

More particularly, this invention relates to a method for reducing the size of beryllium metal particles through suitable milling, or grinding, techniques to a size below about 200 mesh and, more particularly, to sub-sieve weighted average particle sizes down to about 1 micron, and wherein the beryllium metal particles are substantially devoid of beryllium oxide when produced and are of a fragmented configuration.

The search for methods capable of producing very fine beryllium metal particles has become increasingly important due to the importance and use of beryllium metal powders in solid state propellant fuels as well as in other applications. While beryllium metal powders have heretofore been produced by mechanical milling and grinding techniques, both dry and wet, the methods employed have not been satisfactory due to the fact that the beryllium metal particles oxidize substantially during the comminuting operation.

Not only is there a demand for fine beryllium metal I particles, but there is a need for these metal particles to be as free of oxygen as possible and still capable of handling in atmospheric conditions without the necessity of an inert atmosphere.

When sub-micron beryllium particles of the prior art are used or stored, it is necessary to use an inert atmosphere, either gas or liquid, since at these low micron sizes the beryllium particles are pyrophoric. This limits their use and necessitates the use of equipment which complicates normal procedures of production.

In accordance with the present invention, it is found that sub-sieve beryllium metal powders substantially devoid of beryllium oxide can be produced by subjecting beryllium metal particles in the form of a slurry, comprising dry beryllium, which may be in the form of chips or beads, and a dry neutral non-halogenated oxygen free hydrocarbon, to a milling operation.

These powders produced by the present invention are fragmented particles of a size and nature so as to be substantially devoid of beryllium oxide and capable of being handled and stored under atmospheric conditions without catastrophic oxidation.

The process by which the powder is produced in- 'volves the mechanical breakdown or disintegration of the beryllium metal whereby the powder particles are in fragments.

It is, therefore, a primary object of the invention to provide a novel method of reducing the size of beryllium metal particles so as to produce a beryllium metal powder substantially devoid of beryllium oxide and having a protective surface resistant to catastrophic oxidation and with a minimum of deleterious surface contaminants.

Another object of this invention is to provide a novel method of reducing the size of beryllium metal particles to a size below 200 mesh and more particularly in the sub-sieve range, with the resultant beryllium powders being substantially devoid of beryllium oxide and capable of being handled and worked within the atmosphere and within the usual industrial parameters of temperature, without the necessity of an inert atmosphere, by wet grinding the beryllium particles in a dry, neutral, non-halogenated hydrocarbon vehicle.

A further object of the invention is to provide a beryllium powder substantially devoid of beryllium oxide and capable of being stored and used under atmospheric conditions.

A still further object of the invention is to produce beryllium metal powders of a weighted average particle size of from 1 to 37 microns and of a fragmented configuration which when exposed to atmospheric conditions over long periods of time will not oxidize catastrophically.

The foregoing and other objects of this invention are achieved by charging dry beryllium particles, which may be in the form of chips or beads, together with a quantity of pre-dried, neutral, non-halogenated hydrocarbon such as n-hexane, n-heptane, naphtha or benzene, into a grinding mill, which may be, for example, a ball mill or a rod mill, then grinding the charge for a suflicient length of time to effect the reduction in size of the beryllium metal particles to the desired powder particle size, stripping the solvent from the powder by vacuum drying, and then exposing the resultant powder to air under controlled conditions.

Other objects and advantages of the present invention will become apparent from the following detailed description.

Generally the process of the present invention consists in introducing into a grinding mill a supply of dry beryllium metal which may be in the form of small beads, chips or particles, after which there is added to the mill a selected liquid vehicle which, for the purposes of this invention, is an anhydrous, neutral, non-halogenated hydrocarbon.

The selected hydrocarbon is first passed through a drier, or otherwise suitably dried or completely exhausted of any moisture before it is added to the grinding mill, which may be in the form of a ball mill or a rod mill, as desired. The nature of the mill interiorly and of the balls, or rods, is hereinafter more specifically set forth.

The beryllium metal is then subjected to the grinding operation with the non-halogenated hydrocarbon in the ball or rod mill, after which the slurry is removed from the mill and filtered to separate the powder from the vehicle or in the alternative the vehicle may be removed by decantation. During the grinding operation the mill is cooled by suitable means to dissipate the heat produced by friction and to maintain an ambient temperature within the mill.

The filter cake consisting of beryllium powder obtained from the filtration operation is then further dried, preferably in a heated vacuum drier, to effect a final complete removal or stripping of any remaining solvent from the filter cake. Ordinarily the vapors are recovered in a conventional manner.

After drying, the beryllium powder within the drier, still under vacuum, is cooled to ambient temperature by cooling the drier. Suitable temperature measuring means, such as thermocouples, are provided within the drier to measure the temperature of the powder. After the powder is cooled to ambient temperature, air, which may be atmospheric air, is introduced through suitable valve means into the drier at such a rate that the temperature of the beryllium powder remains substantially constant. Cooling of the drier is continued while the air is being introduced into the drier. By exposing the powder within the drier to air under controlled conditions there is formed upon the powder a protective surface film which, it is found, protects the powder from catastrophic oxidation when exposed to normal atmospheric conditions and temperatures.

By this procedure, there is thus obtained a completely dry fragmented non-pyrophoric beryllium powder reduced to a sub-sieve particle size and wherein the particles are substantially devoid of beryllium oxide.

The grinding operation is preferably carried out in a mill having a beryllium metal lining. While the beryllium metal lining is not as highly resistant to wear as other liners which may be employed with satisfactory results, there is no contamination of the ground particles from a practical standpoint. Any material which might be picked up from the liner by the particles as they are being ground, would only be additional beryllium.

As stated, the use of a beryllium metal liner for the mill is to be preferred. However, other lining materials may be used with satisfactory results such, for example, as a lining of cobalt bonded tungsten carbide, pure tungsten, tantalum or molybdenum. The grinding elements used in the mill may, as previously set forth, be in the form of balls or rods of a suitable material.

As an example, by using a beryllium lined ball mill and tungsten carbide grinding balls, with a dry neutral nonhalogenated vehicle as the liquid media, sub-sieve beryllium powders of the character stated, may be obtained.

Mills having other metal linings and using grinding elements of steel, for example, or steel alloy, are not satisfactory as they contaminate the surfaces of the resultant powder particles, as is shown in the hereinafter set forth tabulation of liquid vehicles and materials used.

In order to obtain sub-sieve beryllium powder of the present invention, the grinding mill lining must have the characteristics of being non-reactive with the beryllium metal, and wear-resistant. Accordingly, by the use of a pure beryllium metal liner, while the wear resistance may not be of the highest order as compared with liners made with the other materials referred to, there is the advantage that any beryllium metal adhering to the particle as they are being ground, would not be a matter for concern as there is no contamination of the powder, or any contamination which might be obtained from the use of the other liner materials referred to, or from the tungsten carbide balls or rods, which mightbe cobalt bonded, is of such a slight degree that it can only be expressed as being of the order of parts per million.

The grinding elements used in the mill, in the form of balls or rods are, preferably, bonded tungsten carbide or such elements may be formed of or consist of uranium oxide, thorium oxide, or tantalum carbide. All of these materials have a high density and are highly wear resistant and also are non-reactive with beryllium materials.

The liquid vehicle, or grinding medium, is a neutral hydrocarbon solvent which provides an atmosphere in the mill which protects the beryllium metal during the grinding operation. Although a neutral atmosphere is desired during grinding the beryllium particles produced are non-pyrophoric and capable of storage and use in ordinary atmospheric conditions. During the grinding operation the attrition temperatures are much higher than the normal ambient temperature and therefore at this time a neutral atmosphere is necessitated to prevent oxidation of the beryllium surface. For this purpose use is made of a naphtha, such a Stoddard solvent, which solvent is commonly used in the dry cleaning industry. Such naphthas are neutral to beryllium and have closed cup flash points about F. Petroleum solvents inherently contain some small degree of moisture which, if not removed, will increase the beryllium oxide content in the powder during the milling operation. However, the use of a completely anhydrous, neutral, non-halogenated hydrocarbon solvent such as benzene, heptane, hexane, naphtha, etc., results in no contamination pick-up and does not render the resultant powder reactive. For the practice of the present invention, these hydrocarbon solvents must be thoroughly predried with effective drying agents such as zeolites, Linde molecular sieves, or ion exchange resins.

As previously set forth, after the milling operation has been carried on or maintained for the desired predetermined length of time, the slurry is removed from the mill and separated from the grinding elements either during the removal operation or subsequently, and the liquid vehicle is then removed either by filtration or decantation. The volatile vehicle which may be retained in the powder mass is then stripped from the mass in a suitable manner as, for example, by a vacuum dryer, after which the powder is cooled to ambient temperature and exposed to air under controlled conditions as hereinbefore set forth.

The following example sets forth in greater detail the production of the sub-sieve beryllium powder in accordance with the method of the present invention.

This example is, of course, illustrative only and is not to be taken as restrictive in any manner, as it will be apparent from the preceding description, changes or variations may be made in the material of the mill, the grinding elements and the liquid vehicle employed as the protective medium for the metal as it is being ground.

Example I 600 pounds of cobalt bonded, /2 inch diameter, tungsten carbride spherical balls were introduced into a 20 gallon total volume beryllium metal mill. A charge of 25 pounds of beryllium metal chips or crushed beads were then introduced into the mill with 3 gallons of pre-dried naphtha. The mill was closed and rotated at about 60% of critical speed for x hours, as set forth in the hereinafter tabulated schedule.

During the rotation cycle, the mill is cooled to ambient temperature by suitable means, in order to dissipate the heat caused by friction.

At the termination of the selected number of hours of operation of the mill the slurry is removed as hereinafter set forth, and the powder material separated by filtration from the naphtha, or other hydrocarbon vehicle which may have been employed, and the filter cake thus obtained, consisting of beryllium powder, is dried by a heated vacuum dryer.

After drying, the beryllium powder within the drier which is still under vacuum is cooled to ambient temperature by cooling the drier. As hereinbefore set forth, suitable temperature measuring means such as thermocouples are provided within the drier to measure the temperature of the powder. After the powder is cooled to ambient temperature, air, which may be atmospheric air, is introduced through suitable valve means into the drier into contact with the powder contained thereimThe rate of introduction of the air is controlled such that the temperature of the powder remains substantially constant. Cooling of the drier is continued during the introduction of the air.

ticles dry. These .tests were made on berrylium particles of a Weighted average particle size of 25 microns produced by a grinding period of about six hours.

It has been found that by exposing the powder within the 5 percent g dn'er to air under controlled conditions that there is formed Type mm Type ban Vehicle ggf g upon the surface of the powder particles a protective sur- 1 Steel Steel None 1.62 face film wh1ch protects the powder from catastroph1c ox1- d g gletbanol 1M6 eetone 11.16 dat1on when exposed to normal atmospheric conditions we Benzene None and temperatures. WG. n-Heptane :None The degree of comminution varies with the milling time $8;- ifgiffifc: 83: as is indicated in the following tabulation, where x stands 9 d g tgel go i g llgone for the hours of operation of the mill.

1 hrs 2 4 6 12 24 32 4s Weighted average particle size (microns). 25 15 10 8 7 +108 mesg 1 56 14 6 -10 mes +200 mesh .1 26 24 12 -200 mesh 18 62 82 30 microns- 92 94 98 100 20 microns. 70 78 9O 94 -10 microns 34 50 60 70 microns 14 26 The foregoing results are expressed in weight percent- Percent Percent age. The symbol represents less than, and the symbol 30 1390 Content Fe content water Soluble represents greater than. Analysis of the foregoing in partwle ce e i p t C data shows that it is possible to operate a continuous wet .1 L002 milling process by continually screening and recycling 83% the plus 200 mesh fraction and obtain as a result a minus 5 ,1 5 200 mesh beryllium powder after stripping the solvent -31: gag: 38% from the minus 200 mesh fraction, which as will be shown 1 one :1 1,10 2 hereinafter, is substantially devoid of beryllium oxide. 5 3 2 83% As indicated above, for the different length of time the material is ground, different particle sizes of beryllium metal are produced. The longer the grinding the smaller the particle. The size of the particles in relation to time of grinding is predictable and can be predetermined. This size is expressed in weighted average particle size which is defined as that point on a curve plotting particle size vs. cumulative weight percent which represents 50 percent of the cumulative weight. Particle size determination is made by Coulter Counter method. Where not otherwise designated, all sizes are meant to be weighted average particle size.

Example II The same procedure was followed as in Example I, except that n-hexane was used instead of naphtha.

Example H1 The same procedure was followed as in Example I, except that n-heptane was used instead of naphtha.

Example IV The same procedure was followed as in Example I, except that benzene was used instead of naphtha.

The following tabulation lists some other vehicles tested in addition to those above named, as well as the materials of construction of equipment employed.

The listing also sets forth the chemical analyses of the resutling powders, showing in the comparison, the result of obtaining a substantially beryllium oxide free surface and freedom of surface iron on particles of the subsieve beryllium powder when employing naphtha, n-hexane, n-heptane, and benzene as the grinding vehicle, as against the undesirable results obtained in the use of acetone or methanol or in the grinding of the beryllium par- 1 Various fractions of petroleum naphthas are satisfactory for use such as, and including, Shell 801335.

2 So small as not to be measurable under oridlnary techniques. Shell Sol 335 is a petroleum solvent distributed by Shell Oil Company, having a closed cup flash point of F. and a distillation range from 305 F. to 336 F.

Broadly any anhydrous, neutral and non-halogenated hydrocarbon is applicable to this process regardless of its boiling point, providing it can be stripped, even under vacuum, from the resulting powder.

With regard to the tabulation setting forth the results of using different types of mills and balls it will be observed that, in dry milling, a considerable percent of beryllium oxide on the surface of the powder particle is formed. This is given as 1.62% of surface beryllium oxide with a beryllium oxide content in the particle of 34%. Surface iron is about 30% with a percentage of .1% in the particle and a water soluble chlorine percentage of less than .002.

With methanol, as set forth, the beryllium oxide surface film is high, being 14.66% with a .37% in the parti cle, with surface iron averaging 1.1% and .10% in the particle and the same percent of chlorine as in the dry milling.

With the acetone and using a steel liner and steel balls, the beryllium oxide surface percentage is also high and the surface content of iron slightly greater than in the use of methanol.

In using the anhydrous non-halogenated hydrocarbons as listed, it will be seen that the sub-sieve beryllium powder particles showed no measurable surface film of beryllium oxide and only the small percentage of about 34% of the beryllium oxide in the particle.

The above data illustrate that it is possible to prepare a beryllium powder with substantially identical chemistry to the starting chip or bead with the use of a beryllium mill and tungsten carbide balls and non-halogenated oxygen free neutral hydrocarbon solvents.

In the hereinbefore set forth examples, and with reference to Example I wherein it is stated that a 20 gallon total volume mill was employed, this mill had an inside diameter of 16.75 inches and is normally operated at a speed of 67 revolutions per minute. Being operated at 60 percent of its critical speed, as set forth in the example, it will be seen that the speed of rotation for the example given, was 40 rpm. However, it is to be understood that the operating speed might be varied without affecting the results obtained.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, and since the scope of the invention is defined by the appended claims, all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents are therefore intended to be embraced by those claims.

We claim:

1. A process of producing beryllium metal powder substantially devoid of beryllium oxide which comprises the following steps:

(1) introducing beryllium metal and an anhydrous,

neutral, non-halogenated hydrocarbon vehicle into a grinding mill, and (2) milling said beryllium metal in the presence of the vehicle, and (3) separating the beryllium metal powder thus produced from the hydrocarbon vehicle. 2. A process as set forth in claim 1 including the additional step of (4) drying said beryllium powder so as to remove any remaining vehicle therefrom. 3. A process as set forth in claim 2 comprising the additional steps of:

(5) cooling said beryllium powder after drying to ambient temperature, and

(6) contacting said beryllium powder with air under controlled conditions.

4. A process as set forth in claim 3 wherein the beryllium powder is cooled while being contacted by air.

5. A process as set forth in claim 4 wherein the air contacting said beryllium powder is introduced at such a rate that the temperature of the beryllium powder remains substantially constant.

6. A process as set forth in claim 1 wherein the grinding mill is cooled during the milling operation.

7. A process as set forth in claim 1 wherein the auhydrous, neutral, non-halogenated hydrocarbon vehicle is selected from the group consisting of benzene, n-heptane, n-hexane, and fractions of petroleum naphthas.

8. A process as set forth in claim 3 wherein the air is atmospheric air.

9. A process of producing beryllium metal powder substantially devoid of beryllium oxide and which is resistant to catastrophic oxidation under normal atmospheric and temperature conditions, comprising exposing beryllium metal powder which has been cooled to ambient temperature to air under controlled conditions While maintaining the temperature of the beryllium metal powder substantially constant.

References Cited UNITED STATES PATENTS 3,322,582 5/1967 Morana et al 175-05 1.. DEWAYNE RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant Examiner U.S. Cl. X.R. l17l00; 241-16 

